1. Field of the Invention
The present invention relates to a conveying device that includes an auto document feeder (ADF), and a printing apparatus that employs this conveying device.
2. Description of the Related Art
A conventional image scanning device equipped with an auto document feeder (hereinafter also referred to as an ADF), disclosed in Japanese Patent Laid-Open No. 2002-271566, includes a document separating/conveying unit, a motor and a controller, and, when a document has been set up in the apparatus, determines whether a motor is overloaded, or overheated and controls the feeding of the document. As a feeding control method, the scanning speed is reduced when the number of sheets of the document that have been fed, or the feeding period, has reached a predetermined value. As another control method, scanning is halted and the document sheets are held in a waiting state, or scanning is prohibited to reduce the temperature of the motor.
An image scanning device of a flat bed type, disclosed in Japanese Patent Laid-Open No. 2001-83621, includes a DC motor as a motor and a rotary encoder as a pulse generator. The speed of a rotor is controlled using a pulse counting unit, and motor stop characteristics that are accompanied by a rise in the temperature of the motor are corrected.
However, the proposal disclosed in Japanese Patent Laid-Open No. 2002-271566 is provided for a stepping motor, and no control method is disclosed for inhibiting a rise in the temperature when a DC motor is employed as a driving source. Further, according to this technique, since the determination as to whether to control a rise in the temperature is made when document sheets have been set, in a case wherein a large number of document sheets is designated as a maximum production specification value that is assumed to be required to perform such a determination, when the scanning of only a small number of document sheets is actually required, the inhibition of a temperature rise must be begun with a determination reference at which no problems will be encountered, even when the maximum number of document sheets have been set. Therefore, availability for the apparatus may be inhibited.
Furthermore, the technique disclosed in Japanese Patent Laid-Open No. 2001-83621 is related to a DC motor temperature rise, and describes the control provided for the speed of movement of a scanning unit, for a flat bed scanning process in which the scanning unit is reciprocated to read a document that has been set on a flat bed, but does not provide a description of how to control or to limit a rise in the temperature of an ADF.
As described above, according to the related art, for an ADF that employs a DC motor as a drive source, inhibiting a rise in the temperature of a DC Motor can not be accomplished by performing a simple, but accurate control procedure consequent with the warming property of the DC motor.